Macroalgae Cultivation & Sinking for Carbon Sequestration

A Framework for Global Research

The need for solutions to the climate crisis has never been more urgent. Wildfires, droughts, heatwaves, food insecurity and resulting migration, and climate-related conflict threaten us all each day. Seas are rising, warming, acidifying, and losing oxygen—all of which threaten the health and structure of marine ecosystems and the communities around the world that rely on them.

Stopping, and eventually reversing, the harms of climate change requires that we simultaneously stop emitting carbon dioxide and remove the existing carbon dioxide pollution from the atmosphere and ocean.

The total quantity of carbon that must be removed depends on temperature targets, but ranges from hundreds to thousands of gigatons of carbon dioxide. The removal requirements are staggering, and thus so too is the need to develop scalable carbon removal solutions.

Ocean-Based Carbon Dioxide Removal

There are many potentially promising ways to clean up carbon dioxide pollution, including those that enhance the ocean’s natural sequestration abilities. Ocean-based carbon dioxide removal pathways offer high potential for meeting carbon dioxide removal goals for several reasons:

The ocean covers 70 percent of the surface area of the planet, providing substantial scalability for effective solutions.
The ocean is already incredibly effective at sequestering carbon through natural processes; it holds about 50 times more carbon than the atmosphere and has sequestered about 30 percent of anthropogenic carbon dioxide emissions since the start of the industrial era.
Ocean-based pathways likely offer greater durability for carbon removal than terrestrial options, such as afforestation, wherein sequestered carbon can be released back to the atmosphere due to disturbance (e.g., wildfire).

Cultivating Macroalgae for Carbon Sequestration

Macroalgae, or seaweed, are highly productive marine species that transform carbon in seawater into seaweed biomass. Recently, proposals have emerged to cultivate macroalgae and then sink the biomass to the deep ocean in order to sequester the carbon inside.

In theory, this would allow the ocean to remove additional carbon dioxide from the atmosphere. While still in its infancy, macroalgal cultivation technology has attracted serious attention and early-stage investment. However, there exists very little information about the effectiveness and environmental impacts (both beneficial and detrimental) from which to assess its feasibility, suitability, and risks. Beyond a small number of modeling studies, and studies of natural systems that exhibit similar behavior, we collectively lack the information necessary to make well-informed decisions about the efficacy and impacts of this technology.

Designing a Framework for Global Research

Together with the Monterey Bay Aquarium Research Institute, Ocean Visions convened a working group consisting of members across academia, government, and industry to improve the understanding of the effectiveness and consequences of sinking seaweed to the deep ocean for long-term carbon sequestration.

This working group designed a globally applicable research framework intended to guide controlled field trials, observational, laboratory, and modeling efforts needed to estimate the effects of seaweed sinking programs at ‘climate-relevant’ scales (e.g., megatons or gigatons of carbon per year).

The report, published in October 2022, provides the following:

A comprehensive list of all scientific questions that need to be answered, along with recommended scientific approaches for answering those questions.
Detailed guidance on experimental designs for controlled field trials.
Estimates of the cost of field trials and the cost of a global research program consisting of multiple field trials.
Budgeting tool to support resource allocation for field experiments.
Table of oceanographic assets, infrastructure, and pilot projects to support research facilitation.
Accompanying this report is a searchable, interactive database of funding opportunities for those seeking to undertake the science and engineering priorities identified in the report. Learn more about the database of funding opportunities.

Access the Research Brief, Full Report, Budgeting Tool, and Database of Funding Opportunities

Working Group

Coordinating Authors:

David Koweek is the Science Director of Ocean Visions.
Jim Barry is a Senior Scientist and Benthic Ecologist at the Monterey Bay Aquarium Research Institute.
Sarah Mastroni is the Program Officer at Ocean Visions.

The report was developed through structured discussion with a diverse group of thought leaders:

Joan Alfaro-Lucas is a Postdoctoral fellow at the University of Victoria, Canada.
Dror Angel is an applied marine ecologist at the Department of Maritime Civilizations and the head of the Laboratory of Applied Marine Biology & Ecology Research (AMBER), Charney School of Marine Science and the Recanati Institute for Maritime Research at the University of Haifa, Israel.
Mark E. Capron is the President of OceanForesters, an international engineering and scientific consulting firm.
Meg Chadsey is an Ocean Acidification Specialist with Washington Sea Grant & a Sea Grant Liaison to NOAA Pacific Marine Environmental Laboratory.
Max Chalfin is the Director of Research at Running Tide Technologies.
Stephen Crooks is the Co-Founder at Silvestrum Climate Associates, Co-Founder/Principal at Wetland Science and Coastal Management, and Research Associate at the Smithsonian Institution.
Kristen Davis is an Associate Professor of Civil and Environmental Engineering and an Associate Professor of Earth System Science at UC Irvine.
Colleen Durkin is a Scientist at the Monterey Bay Aquarium Research Institute.
Mar Fernández-Méndez is a Junior Professor of Polar Biological Oceanography at the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research.
Brian von Herzen is the Founder and Executive Director of the Climate Foundation and is the founder of the Marine Permaculture Alliance.
Jordan Hollarsmith is the Mariculture and Macroalgae Lead Research Biologist at the Alaska Fisheries Science Center (National Oceanic and Atmospheric Administration, National Marine Fisheries Service).
Gi Hoon Hong is a professor of marine biogeochemistry at the East China Normal University and the Strategy Director of the Integrated Marine Biosphere Research (IMBeR).
Nico Julian is the Founder and CEO of Phykos, an ocean-based carbon removal company.
Amanda Kahn is an Assistant Professor at Moss Landing Marine Laboratories/San Jose State University and is a ‘scientist ashore’ with the Nautilus exploration program.
Marc von Keitz (observer) is the Director of the Grantham Foundation for the Protection of the Environment and was previously a Program Director of the Advanced Research Projects Agency-Energy (ARPA-E).
Lisa Levin is a Distinguished Professor emeritus of biological oceanography at Scripps Institute of Oceanography, University of California San Diego.
Matthew Long is an Oceanographer at the National Center for Atmospheric Research.
Alyson Myers is the President of the Fearless Fund, an ocean research organization, and an awardee of the U.S. Department of Energy Advanced Research Projects Agency-Energy’s (DOE ARPA-E) Macroalgae Research Inspiring Novel Energy Resources (MARINER) program.
Chioma Nwakanma is an Associate Professor at Michael Okpara Federal University of Agriculture in Umudike, Nigeria.
Morgan Raven is an Assistant Professor of Earth Sciences at UC Santa Barbara.
Aurora M Ricart is a Postdoctoral Researcher at the Bodega Marine Laboratory of the University of California, Davis, and at the Bigelow Laboratory for Ocean Sciences.
Neil Sims is the Founder and CEO of Ocean Era.
Tanja Stratmann is a postdoctoral researcher at the Royal Netherlands Institute for Sea Research in the Netherlands.
John Taylor is a Professor of Oceanography at the University of Cambridge and a Fellow of St. John’s College.
Chris Vivian (observer) is a Co-Chair of GESAMP Working Group 41 on ‘Ocean interventions for climate change mitigation’ and was a Senior Scientist at the Centre for Environment, Fisheries and Aquaculture Science in the UK.